Reject handle types in 'map' value type

design/mvp/Binary.md

@@ -260,6 +260,8 @@ Notes:
   rejects any transitive use of `borrow` in an exported value type.
 * Validation of `stream` and `future` rejects element types that transitively
   contain a `borrow`.
+* Validation of `map` rejects value types that transitively contain an `own`,
+  `borrow`, `future`, `stream` or `error-context`.
 * Validation of `stream` rejects `(stream char)` as a temporary
   [TODO](Concurrency.md#TODO).
 * Validation of `resourcetype` requires the destructor (if present) to have

design/mvp/Explainer.md

@@ -862,7 +862,11 @@ original list defines the final value of the key. However, bindings generators
 are not *required* to deduplicate keys and may instead simply present the
 original list to guest code. To simplify bindings generation, `<keytype>` is a
 conservative subset of `<valtype>`, but this subset could be expanded over time
-based on use cases.
+based on use cases. Similarly, validation currently rejects `(map K V)` when `V`
+transitively contains an `own`, `borrow`, `future`, `stream` or
+`error-context`, since dropping the value of a duplicate key would otherwise
+require bindings generators to correctly dispose of the contained handles. This
+restriction could be relaxed in the future.
 
 Note that, at least initially, variants must have a non-empty list of
 cases. This could be relaxed in the future to allow an empty list of cases, with

design/mvp/WIT.md

@@ -1963,6 +1963,8 @@ meanings though so they're also provided as first-class types.
 values but is meant to be represented by bindings generators in the source
 language as a mapping from keys to values (e.g., as an associative array or or
 hash table) where, in the case of duplicate keys, the last key's value is used.
+Currently, the value type of a `map` may not transitively contain an owned or
+borrowed handle, `future`, `stream` or `error-context`.
 
 The `future` and `stream` types are described as part of the [concurrency
 explainer](Concurrency.md#streams-and-futures).

test/nyi.txt

@@ -3,3 +3,4 @@
 ./values/post-return.wast
 ./async/big-interleaving-test.wast
 ./async/forward.wast
+./validation/map.wast

test/validation/map.wast

@@ -0,0 +1,85 @@
+;; (map K V) validation
+
+(component definition
+  (type (map bool u8))
+  (type (map s8 u8))
+  (type (map u8 u8))
+  (type (map s16 u8))
+  (type (map u16 u8))
+  (type (map s32 u8))
+  (type (map u32 u8))
+  (type (map s64 u8))
+  (type (map u64 u8))
+  (type (map char u8))
+  (type (map string u8))
+  (type (map string f64))
+  (type (map string string))
+  (type (map string (list u8)))
+  (type (map string (tuple u8 string)))
+  (type (map string (record (field "a" u32) (field "b" string))))
+  (type (map string (variant (case "a") (case "b" u32))))
+  (type (map string (enum "x" "y")))
+  (type (map string (flags "p" "q")))
+  (type (map string (option string)))
+  (type (map string (result u32 (error string))))
+  (type (map string (map u32 (list string))))
+  (type (list (map string u32)))
+  (type (option (map u32 string)))
+  (type (stream (map string u32)))
+  (type (future (map string u32)))
+  (type (func (param "m" (map string u32)) (result (map u32 string))))
+)
+
+(assert_invalid
+  (component (type (map f32 u8)))
+  "invalid map key type")
+(assert_invalid
+  (component (type (map (list u8) u8)))
+  "invalid map key type")
+(assert_invalid
+  (component (type (map (tuple u8 u8) u8)))
+  "invalid map key type")
+(assert_invalid
+  (component
+    (type $R (resource (rep i32)))
+    (type (map (own $R) u8)))
+  "invalid map key type")
+(assert_invalid
+  (component
+    (type $R (resource (rep i32)))
+    (type (map u32 (own $R))))
+  "map value type cannot contain a handle")
+(assert_invalid
+  (component
+    (type $R (resource (rep i32)))
+    (type (map string (option (borrow $R)))))
+  "map value type cannot contain a handle")
+(assert_invalid
+  (component
+    (type (map string (record (field "f" (future u8))))))
+  "map value type cannot contain a handle")
+(assert_invalid
+  (component
+    (type (map u8 (list (stream u8)))))
+  "map value type cannot contain a handle")
+(assert_invalid
+  (component
+    (type $FT (future))
+    (type (map char (variant (case "a") (case "b" $FT)))))
+  "map value type cannot contain a handle")
+(assert_invalid
+  (component
+    (type $R (resource (rep i32)))
+    (type $Rec (record (field "r" (own $R))))
+    (type (map u32 $Rec)))
+  "map value type cannot contain a handle")
+(assert_invalid
+  (component
+    (type $R (resource (rep i32)))
+    (type (map string (map string (tuple u32 (own $R))))))
+  "map value type cannot contain a handle")
+(assert_invalid
+  (component
+    (import "r" (type $R (sub resource)))
+    (import "f" (func (param "m" (map string (own $R))))))
+  "map value type cannot contain a handle")